Could you please elaborate a bit as if you are right, then I think I missing something?
As far as I can see the vpuenc_h264 element only has the following properties: gop, bitrate, quant and stream_slice_count and force_idr in the latest version.
There is no pixel-aspect-ratio property on it.
As far as I can see, the underlying libraries imx-vpu-hantro and imx-vpuwrap do not seem to expose this parameter on their API, so I am not sure how such GStreamer attribute could propagate its way down to the H1 library, but maybe I am missing something.
Other GStreamer elements do have a pixel-aspect-ratio property, like rawvideoparse, but it has nothing to do with NXP nor the VPU. I would be reluctant to use rawvideoparse as I would be concerned for the cost of the additional processing it may require.
**EDIT**
The GStreamer element vpuenc_h264 relies on the OMX IL API which as far as I can see currently does not provide a way to set the pixel aspect ratio. In fact, the API is rather limited in what it exposes. Although this feels wrong, I think I will have to modify the imx-vpu-hantro library... which leads me to my next question: why is this library provided as a .bin archive instead of being pulled from a git repo?
